Electrodeposition, although known for some time, has only recently become of commercial importance as a coating application method. Along with the increased use of such methods has been the development of certain compositions which can provide satisfactory coatings when applied in this manner. While many compositions can be electrodeposited, most coating compositions when applied using electrodeposition techniques do not produce commercially usable coatings. Moreover, electrodeposition of many coating materials, even when otherwise successful, is attended by various disadvantages such as non-uniform coatings and by poor throwing power. In addition, the coatings obtained are in most instances deficient in certain properties essential for their utilization in many applications for which electrodeposition is otherwise suited. In particular, properties such as corrosion resistance and alkali resistance are difficult to achieve with the resins conventionally employed in electrodeposition processes. This is especially true with the conventional electrodeposition vehicles, which contain polycarboxylic acid resins solubilized with a base; these deposit on the anode and because of their acidic nature tend to be sensitive to common types of corrosive attack, e.g., by salt, alkali, etc. Many electrodeposited anodic coatings are subject to discoloration or staining because of dissolution of metal ions at the anode.
Epoxy resins are among the most useful resins for many purposes and have excellent corrosion resistance and other properties. They are employed in many coatings, but have not been employed in water-dispersible compositions suitable for application by electrodeposition because they cannot be adequately dispersed in water under the conditions required in such processes. Esterified epoxies have been utilized, but these act similarly to the polycarboxylic acid resins, and while offering many advantages over such polycarboxylic acid resins, are still subject to many of their disadvantages.
In copending application Ser. No. 772,353, filed on Oct. 31, 1968, now U.S. Pat. No. 3,619,398, there are described certain water-dispersed epoxy compositions which can be electrodeposited with good results. These compositions are typically stable emulsions and although they are very useful and provide highly desirable coatings they are still subject to certain disadvantages, such as low throwing power and difficulty in controlling film thickness, attributed to the hydrophobic nature of the epoxy reaction products therein.
In copending application Ser. No. 100,834, filed Dec. 22, 1970, there are disclosed cathodic electrodepositable epoxy resins containing epoxy groups, quaternary ammonium salts, boron and oxyalkylene groups and aqueous dispersions thereof.